1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method for forming seal patterns in an LCD device while improving a device yield.
2. Discussion of the Related Art
With the expansion of the information society, a need has arisen for displays capable of producing high quality images in thin, lightweight packages and that consume little power. To meet such needs, research has produced a variety of flat panel display devices, including liquid crystal displays (LCD), plasma displays (PDP), electro luminescent displays (ELD), and vacuum fluorescent displays (VFD). Some of these display technologies have already been applied in information displays.
Of the various types of flat panel display devices, LCD are very widely used. In fact, in portable devices, such as notebook PC computers, LCD technology has already replaced cathode ray tubes (CRT) as the display of choice. Moreover, even in desktop PCs and TV monitors, LCDs devices are becoming more common.
Despite various technical developments in LCD technology, however, research in enhancing picture quality of LCD devices has been lacking compared to research in other features and advantages of LCD devices. Therefore, to increase the use of LCD devices as displays in various fields of application, LCD devices capable of expressing high quality images (e.g., images having a high resolution and a high luminance) with large-sized screens, while still maintaining a light weight, minimal dimensions, and low power consumption must be developed.
LCDs generally include an LCD panel for displaying an image and a driving part for providing driving signals to the liquid crystal display panel.
Typically, LCD panels include first and second glass substrates bonded to each other while being spaced apart by a cell gap, wherein a layer of liquid crystal material is injected into the cell gap.
The first glass substrate (i.e., thin film transistor (TFT) array substrate), supports a plurality of gate lines spaced apart from each other at a fixed interval and extending along a first direction; a plurality of data lines spaced apart from each other at a fixed interval and extending along a second direction, substantially perpendicular to the first direction, wherein pixel regions are defined by crossings of the gate and data lines; a plurality of pixel electrodes arranged in a matrix pattern within respective ones of the pixel regions; and a plurality of thin film transistors (TFTs) capable of transmitting signal from the data lines to corresponding ones of the pixel electrodes in response to a signal applied to respective ones of the gate lines.
The second glass substrate (i.e., color filter substrate) supports a black matrix layer for preventing light leakage in areas outside the pixel regions; a color filter layer (R, G, B) for selectively transmitting light having predetermined wavelengths; and a common electrode for displaying a picture. Common electrodes of In-Plane Switching (IPS) mode LCD devices, however, are formed on the first substrate.
Uniformity of the cell gap is maintained by spacers arranged between the first and second glass substrates, which are bonded together by a seal pattern. The seal pattern includes a liquid crystal injection inlet allowing liquid crystal material to be injected into the cell gap. Upon injecting liquid crystal material into the cell gap via the liquid crystal injection inlet, the layer of liquid crystal material is thus formed.
The layer of liquid crystal material is driven (e.g., light transmittance characteristics of the layer of liquid crystal material are controlled) according to electric fields generated between the first and second substrates by the pixel electrode and the common electrode. By controlling the light transmittance characteristics of the layer of liquid crystal material, pictures may be displayed.
To form the aforementioned layer of liquid crystal material, related art manufacturing methods incorporate a liquid crystal injection method wherein a pressure difference is created between the cell gap and a vacuum chamber and liquid crystal material is injected into the liquid crystal injection inlet via a capillary phenomenon. A method for manufacturing the related art LCD device incorporating the liquid crystal injection method will now be described.
The first substrate (i.e., a TFT array substrate), supporting the TFTs and pixel electrodes, and the second substrate (i.e., the color filter substrate), supporting the black matrix layer, color filter layer, and common electrode, are provided. Next, spacers are dispersed on the TFT array substrate to maintain a uniform cell gap between the two substrates. A seal pattern is then formed at a periphery of the other of the two substrates to prevent liquid crystal material from leaking and to bond the two substrates together. The seal pattern is typically formed of a thermo-hardening material such as an epoxy including a mixture of an epoxy resin and an initiator. Next, a heat treatment is performed to bond the TFT array and color filter substrates to each other. When performing the heat treatment, the epoxy resin within the epoxy seal pattern is activated by the initiator and becomes a highly cross-linked polymer. As a result, the epoxy seal pattern functions as the seal pattern having suitable adhesion characteristics.
Subsequently, the bonded substrates are placed in a vacuum chamber, wherein the cell gap between the bonded substrates is maintained in a vacuum state, and dipped into a reservoir of liquid crystal material. Since a vacuum is maintained within the cell gap, liquid crystal material is injected into the cell gap by a capillary phenomenon. After a predetermined amount of liquid crystal material has been injected into the cell gap, nitrogen gas (N2) is pumped into the vacuum chamber, so that liquid crystal material is injected into regions of the cell gap not previously injected into, according to the pressure difference between the cell gap and the pressure within the vacuum chamber having the pumped nitrogen gas (N2). As a result, the layer of liquid crystal material is formed between the bonded TFT array and color filter substrates.
FIG. 1 illustrates a plan view illustrating a related art LCD device.
Referring to FIG. 1, the first substrate (i.e., the TFT array substrate) supports a plurality of gate lines 11 spaced apart from each other at a fixed interval and extending along a first direction and a plurality of data lines 12 spaced apart from each other at a fixed interval and extending along a second direction, substantially perpendicular to the first direction. Pixel regions P are defined by crossings of the gate and data lines 11 and 12, respectively. A plurality of pixel electrodes 16 are arranged in a matrix pattern within respective ones of the pixel regions P, and thin film transistors are formed at crossings of the plurality of gate and data lines 11 and 12, respectively. In response to signals applied from the gate lines 11, the thin film transistors transmit signals applied from the data lines 12 to respective ones of the pixel electrodes 16.
Each the thin film transistor includes a gate electrode 13 protruding from a corresponding gate line 11, a gate insulating layer (not shown) formed over an entire surface of the first substrate 10, a semiconductor layer 15 formed on the gate insulating layer in a region above the gate electrode 13, a source electrode 15a protruding from a corresponding data line 12, and a drain electrode 15b formed opposite the source electrode 15a by a predetermined distance and electrically connected to the pixel electrode 16 through a contact hole 17.
The second substrate (i.e., the color filter substrate; not shown) supports a black matrix layer having openings in regions corresponding to the pixel regions P of the first substrate 10 and prevents light leakage; an R/G/B color filter layer for selectively transmitting light having predetermined wavelengths; and a common electrode for driving the layer of liquid crystal material with the pixel electrodes 16.
The first substrate 10 is bonded to the second substrate (i.e., the color filter substrate), wherein the two substrates are spaced apart from each other by a predetermined distance, uniformly maintained by spacers. The first and second substrates are bonded to each other using a seal pattern having a liquid crystal injection inlet. Upon injecting liquid crystal material into the cell gap via the liquid crystal injection inlet, the layer of liquid crystal material is thus formed.
FIG. 2A illustrates a method of forming a seal pattern according to a screen printing method.
Referring to FIG. 2A, a screen printing apparatus includes a one piece screen mask 32 having an opening 31 for selectively exposing a seal pattern region and a squeegee 33 for forming the seal pattern on the first substrate 10 by selectively providing sealant material to the first substrate 10 via the screen mask 32. After arranging the one piece screen mask 32 on the first substrate 10, sealant material is disposed and the seal pattern is formed on the first substrate 10 in regions corresponding to the opening 31 by rolling a squeegee 33 over the first substrate 10 along the arrow direction in the drawing. Next, solvent within the seal pattern is evaporated in a drying process for leveling. Further, the seal pattern includes a liquid crystal injection inlet at one side thereof and is arranged at a periphery of a picture display region to prevent liquid crystal from leaking.
The aforementioned related art screen printing method is a relatively simple process to perform. However, use of the aforementioned related art screen printing method is problematic because the amount of sealant material used can be excessive. More specifically, while sealant material is disposed over the entire surface of the screen mask 32, only a small portion of the disposed sealant material is actually incorporated into the seal pattern by the squeegee 33. Further, the screen mask 32 contacts the first substrate 10. Such contact generates defects within an alignment layer (not shown) formed on the first substrate 10 because the screen mask 32 damages the alignment layer. Accordingly, a picture quality of the related art LCD device becomes deteriorated.
Further, when seal patterns are formed according to the aforementioned related art screen printing method, the size of a one piece screen mask is often limited to a predetermined, maximum size. Therefore, it becomes difficult to effectively use remaining portions of large-sized base substrates (i.e., portions of substrate within which LCD panels are not formed), and the cost of manufacturing LCD panels grows excessively. Further, the size of the related art one piece screen mask must be increased in accordance with the size of the LCD panel. As the size of LCD panels increases, the size of the related art one piece screen masks also increase, thereby making the related art one piece screen mask difficult to maintain and handle.
In order to solve the problems arising from use of the aforementioned related art screen printing method, a seal dispensing method has been proposed.
FIG. 2B illustrates a method of forming a seal pattern according to a dispensing method.
Referring to FIG. 2B, the first substrate 10 (i.e., the TFT array substrate) is loaded onto a stage (not shown) capable of moving in many directions. Next, sealant material 7 is selectively dispensed along the periphery of the first substrate 10 via a syringe apparatus 34. Though not shown in FIG. 2B (or 2A), the seal pattern 7 typically includes a main seal pattern and a dummy seal pattern wherein the dummy seal pattern is formed to protect the main seal pattern and to prevent liquid crystal material from leaking. Upon selectively dispensing sealant material along the periphery of the first substrate 10, a seal pattern is formed along the periphery of the first substrate 10. Using the aforementioned related art dispensing method, the amount of sealant material used may be decreased compared to the aforementioned related art screen printing method since sealant material is selectively dispensed along the periphery of the first substrate 10. Further, the syringe apparatus 34 does not contact the first substrate 10 such that damage to the alignment layer is substantially avoided and the picture quality of the LCD device is improved.
Use of the aforementioned related art dispensing method of forming the seal pattern becomes problematic, however, when the size of the first substrate increases, or when a size of a picture display area of the LCD panel changes (e.g., upon a model change of the liquid crystal display panel). In light of recent demand for liquid crystal display panels having increased size, the size of the first substrate has also increased. Accordingly, positions where seal patterns are formed on the substrate must change. In the aforementioned related art dispensing method, if the positions where the seal pattern is formed on the substrate changes, the syringe apparatus must be disassembled and reassembled. As the size of liquid crystal display panels increase, the amount of time required to dispense a seal pattern having an increased size also increases. Accordingly, the tact time increases and the device yield of the dispensing method decreases.